Spark-plug



H. THOMAS.

SPARK PLUG. APPLICATION FILED OCT. 6, 1919.

Patented June 14, 1921.

UNITED! STATES PATENT orr cr.

HERBERT 'rnouas, or CHICAGO, ILLINoIs, ASSIGNOR T0 ECLIPSE MANUF CTURING co rANr, or INDIANAPOLIS, INDIANA, A CORPORATION or INDIANA. 1

SPARK-PLUG.

Specification of Letters l atent. Patented June 14, 1921.

Application filed October 6, 1919. Serial No. 328,742.

To all whom it may concern:

Be it known that I, HERBERT THOMAS, a

citizen of the Ynited States, residing at Chisevere operating conditions such as are encountered in airplane work.

I have discovered that one important cause of, the failure of spark plugs in work of thisclass is due two-the leakage of gases occurring through the joints of the plu and upon investigating the cause further find that the heating and cooling of the plug causes contraction and expansion of the parts which finally results in a loosening of the gland which is threaded into the body or shell of the plug whereby these parts are unthreaded to a slight extent permitting the said leakage. After a plug once begins to permit of leakage of this character, even in minute amounts the plug quickly becomes destroyed or at least worthless for further service. V f

I propose to prevent this cause of failure of the plugs by means which forms the subject matter of the present invention. In manufacturing the plugs I preferably form the parts as shown in my co-pending a plication. Serial Number 280.699, filed l\ arch 5, 1919. employing a copper gasket between the body of porcelain and the metallic shoulders which engage it. these copper gaskets serving the dual function of transmitting heat and of forming a yielding seating means. 'hen the plug is properly assembled the threaded. gland member is screwed down in the shell with great force to form a proper seating between the engaging parts and thereafter the gland and the shell are positively locked together by means which will not permit of accidental or ready man- 'ual separation. In other words. I assemble the plug in proper condition for use and then positively, lock the parts together so that neither by accident nor by design can these parts be separated to destroy the correct setting of the spark gap or the proper assembly of the parts.

The particular means which I have shown is not the only means which may be employed within the purview of my invention, but is the preferred means, which I find simple, inexpensive and reliable.

It is highly undesirable to have the parts of the plug separated after they are once assembled, because by the act of setting the porcelain against the copper gaskets these copper gaskets are hardened byv the flow which occurs informing a proper fit between the parts and if the plug is thereafter taken apart, proper reassembly under such conditions is a practical impossibility. The

importance of proper. setting of the electrodes and the proper seating of the gaskets is only beginning to be appreciated by those skilled in the art. It is found that very great improvement in the working of an internal combustion engine, particularly of the high compression type, can be effected by proper design and construction of the spark plugs.

In order to teach those skilled in the art how to practise my invention I shall now refer to the accompanying drawing inwhich the single figure illustrates a vertical section of a plug embodying my invention. The

plug of my invention comprises an outer shell member 1. which is preferably formed with hexagonal faces at the upper surface as indicated at :2 for the purpose of threading the plug into the head or other part'ofthe engine. The lower portion of the shell is reduced to form the: threaded portion 3 which is threaded into the head or other part of the engine as above indicated. A

shoulder 4 is formed on the outside of the shell at the point where this reduction occurs and this shell is adapted to seat against a copper gasket when properly set in the cylinder head :which is indicated in dotted lines'by the reference numeral'6. This copper gasket 5 is formed of soft copper when it is first a plied. and upon threading down the plug t is gasket becomes hardened by flowing to make proper fitbetween the contour of the two engaging parts. The upper inner surface of the sliell 1 is threaded as indicated at 6 to receive the gland member the threaded portion 6. At the lower end ofthe threaded portion 6 I provide a fairly wide shoulder 9 which is adapted to engage the enlarged ring or shoulder 10 of the porcelain member 11 which forms the insulation between the two electrodes as wil be described later. i

The' porcelain plug 11 extends below the enlarged part or shoulder 10, as shown at 12. This extending portion 12 is made of slightly smaller diameter than the bore 13 of the lower part of the shell. A central electrode member 14 extends down through the body of. porcelain 11, being provided witlra sloping shoulder 15 and a rounded spherical point 16 which forms the extremity of this electrode member. Between the slopingshoulder 15 and the lower end 12 of the porcelain plug I provide a gasket 16 of copper to form a seal between the electrode member and the porcelain plug.

The porcelain plug 11 is gripped between the shoulder 9 of the shell 1 and the lower end of the gasket 7 with soft copper gaskets interposed between the porcelain and the metal. The gasket 1? lies between the shoulder 9 and the lower shoulder on the enlarged portion 10 and three copper gaskets 18 lie between the lower edge of the gland 7 and the upper shoulder of the enlarged portion 10. I have shown three thin copper gaskets at this point, but it is obvious that this number may be varied, the sole purpose being to provide asoft conducting gasknown in the art.

ket which will permit the transmission of heat and the proper seating of the parts in engagement with each other.

Between the inner surface of the gland T and the outer cylindrical or conical surface of the plug 11 I provide a sleeve of insulation 19 for preventing the transmission of heat between the gland 7 and the porcelain 11. This sleeve of insulation is preferably made by wrapping a thin sheet of asbestos paper to the desiredthickness about this portion of, the plug.

The upper end of the electrode member 14 is threaded and a terminal nut 20 is threaded to the upper end, thereof to hold the electrode member properly in place in the porcelain 11. The terminal member 20 is provided with a groove 21 to which a sprlng fastener may be secured as is well A copper gasket or washer 22 lies against theupper end of the porcelain 11 and a spring washer 23 isclainped between the terminal nut 20 and the copper washer 22 to hold the nut 20 against possible movement and to take, up the strain of contraction and expansion to the desired degree. I have also found it to be advantageous to pin the terminal nut 20 to the upper threaded end 10 of the elec trode member 14 as by me'ans of the pin 24, After the nut ,20 -1s properly drawn 'which extends out radially from the lower edge of said nut. This flange performs a dual function, namely that it serves to dissipate the heat of the electrode member 14 and it performs the mechanical function of permitting the nut 20 to be properly drawn up on the threads at the upper end of the electrode member 14. The flange 25 is made thick enough so that it can be gripped by a suit-able tool at its outer periphery for drawing up the nut on the threads to make a tight joint. The periphery of the flange 25 may be made round, hexagonal, or in any shape desired.

The spherical tip 16 of the electrode member 14 projects into close proximity with a cross electrode member 26 which is formed of a transverse pin passed through a hole in the threaded portion 3 of the lower end of the shell. This pin 26 and the electrode member 11 with the sphericaltip member 16 are preferably formed of Monel metal. as I find this to be superior for work of this class.

The spherical electrode 16. in cooperation with the cylindrical pin 26 performs the important function as set out in my prior application. of localizing the spark within the small chamber formed by the threaded extension 3 so that firing of the mixture within the small chamber 27 defined within said extension, shoots a flames out into the cylinder to give quick snappy ignition.

After the parts are assembled as indicated in the drawings, the gland 7 is threaded as tightly as possible into the threaded portion 6 so as to grip the enlarged portion 10 of the porcelain plug under high gressure between the gaskets 1'7- and 18; he setting of the gap between the electrodes 16 and 26 is then determined for the proper value and the plug is then in the best posslble condition for use. In order to fix the parts in this condition I thereupon drill a hole through the upper end of the threaded shell 1 and into the threaded part of-the gland member 7. I provide the drill with a suitable stop so that the hole will be drilled short of the paper heat insulation 19. Thereupon I press the'pin 29 into the drilled hole, this pin being provided with a rounded nose so that it may bereadily forced into position but-held against anyefi'ort to dislodge it. The pin 28 is made of such a length that it will substantially fill the. hole just short of striking the bottom of the same. It is possible to shear the pin 28 off by great effort,

but it is intended that the pin 28 positively lock the gland and the shell together in such a manner that they cannot be accidentally and to provide the same, I consider that all means for demonstrating the plugs on government airplanes, that the gland, unless fastened, tends to back off and allow the firing pressure to leak by the seat of the porcelain against the shell or the gland. 'Unless the gland is locked in place by some after the plug is assembled, such leaks will be caused and the seat in a short time is burned out at the gasket and the insulation is either injured or destroyed, with the consequence that the plug is valueless. It is essential to the durability and dependability of a spark plug that a tight seat be maintained at all times in the operation of the plug on the engine. I have discovered that it is essential to the production of a reliable and dc pendable plug that the gasketbe screwed down under heavy pressure in order to secure a gas tight seat between the porcelain and the shell of the plug and then positively and finally locked in position so that no change of the seat can occur and no accidental or intentional change of the setting of the spark gap. There may be other means of locking the gland to the shell besides the means which I have indicated. but as I am the first to discover the cause of the difliculty proper remedy for the permanently locking the gland and the shell tohei come within the scope of my inven t on. By this means it is possible, in a twosuch method. as I have indicated,

ider head or other similar pieceplug, to produce the same effect and the large security of operation heretofore obtained only in a one-piece plug which could not become loose on the seat mechanically after it was once assembled.

I claim:

In combination, a metallic shell having its lower end threaded to screw into the cylinpart of the engine and having an internal shoulder, the interior surface being threaded above said shoulder, a body of insulation having an enlarged portion engaging said shoulder, a wrappin of insulating -material about the body 0 insulation above the enlarged portion, a gland surro unding said wrapping of insulating material and threaded into theupper partof the shell engaging the enlarged part of the insulation against the shell in the shoulder with a gas tight fit, a hole being drilledthrough the shell and through the gland just short of the wrapping, and a pin'pressed into the hole and flush with the oute'r'surface of the shell to hold the gland against loosening in the shell, whereby the gas tight fit between the body of insulation and the shell is preserved and the proper setting of the electrodes" is maintained.

In witness whereof. I hereunto subscribe my name this 2d day of October, 1919.

HERBERT THOMAS.

and holding the same 

